Every single roaming test had one of two problems with watching the
state change between roaming --> connected. Either the test used
wait_for_object_condition to wait for 'connected' which could allow
other states in between. Or it simply used an assert. The assert
wouldn't allow other state changes, but at the cost of potentially
failing due to IWD not having made it to the 'connected' state yet.
Now we have wait_for_object_change which takes two conditions:
initial (from_str) and expected (to_str). This API will not allow
any other conditions except these, and will wait for the expected
condition before continuing. This allows roaming test to reliably
wait for the roaming --> connected state change.
